Bleaching of textile materials is, undeniably, an importantstep in the fabric preparation. Under-bleaching

of fabrics result in poor colour value after dyeing of thefabrics, while over-bleaching causes tendering of the fibres with drasticreductions in the tenacity and degrees of polymerisation. Conventionalhazardous bleaching agents are replaced by many safe chemicals and enzymes;however, the conventional bleaching agents still find a predominance in fabricpreparation.


Natural colour of cotton fibres


Various reasons of natural colour present in the raw cottonfibres are classified into four groups namely, dirt, fibre geometry andmorphology, intrinsic and extrinsic colours50. Change in reflectancevalues due to removal of dirt is not great, but plays a significant role in thelower grades. Fibre geometry or morphology refers to degree of convolutions,cross sectional shape that has proven effects on reflectance of fabrics34.


Postulations of intrinsic colour, inherent and geneticcolour, attributed to the variety of seeds and amorphous mixtures of nitrogencontaining compounds, soluble and insoluble in alcohol, were subsequentlyreplaced, by two theories. First concept is attributed to flavones,orange-yellow pigments that usually occur in the form of glucosides and, secondpossible reason colouring matter is chlorogenic acid, usually isolated fromcoffee bean that acts as a precursor of the pigment. After opening of thecotton boll in the plant, reflectance value gradually decreases because of discolourationdue to fungi growth during weathering of cotton. Alternaria (blackish),Cladosporium (dark brown), and Fusarium moniliforms (near white), isolated fromweathered fibres, flourish under correct weather conditions and appear to beresponsible for discolouration. Suberin, a unique plant cell wall biopolymer,has two distinct chemical domains namely, a poly (phenolic) domain and poly(aliphatic) domain, chemically linked to each other, of which poly (phenolic)domain is associated with lignin present in the plant tissues43, 3.



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About the Author


D Saravananholds MTech Fibre Science & Technology from I Delhi. At present, he is Lectu at Bannari AmmanInstitute Technology, Sathyamangalam, Tamil Nadu. He has published many resepapers, organised seminars conferences.